While mineral oil stocks are a prime source of lubricants, an almost endless list of synthetic lubricants has been developed, including aromatic based lubricant oils, polyesters, polyglycols.
Lubricating oils normally require a variety of additives. The additives usually are classified according to their intended function such as dispersant, oxidation inhibitor, corrosion and rust inhibitor, viscosity-index (VI) improver, pour-point depressant, antiwear agents, antifoam agents, and the like.
Many materials have been prepared for use in lube oils as viscosity index improvers, such as described in U.S. Pat. Nos. 3,554,911 and 3,630,905. 3,994,815 summarizes some of the various hydrogenated arene/conjugated diene copolymers used in the lubricating oil viscosity index improver field.
However, materials soluble in mineral based oils are not necessarily soluble in or effective in synthetic oils, and, materials useful in one class of synthetic oils are rarely suitable or even soluble in other classes.
Problems particularly have arisen with the synthetic poly(.alpha.-olefin) lubricating oils in that many otherwise effective viscosity index improvers are not therein soluble. The synthetic poly(.alpha.-olefin) oils potentially have high value as lube-oils, but needed are effective viscosity index improvers specifically useful therein.
With increased costs of base petroleum stocks, it is highly desirable to find ways to improve poly(.alpha.-olefin oils) and thus hold down costs of the lubricating oils to the American motorist.